Allow FpPrint data to be extended on enrollment.

* Allow FPI_PRINT_NBIS to be extended rather than overridden if a user
  supplies an existing FpPrint template with data;
* Prints will only be extended if a device has the required feature.
  For image-based devices this feature is added by default since they
  typically do not have storage (this can be overridden at the child
  class level).

Extending an existing FpPrint requires passing a template print with
existing data during the enrollment process. This is done because the
caller is responsible for maintaining the fingerprint database and doing
the necessary deserialization operations if needed. The existing
example program is updated to show how to do that.

examples/enroll.c

@@ -35,6 +35,7 @@ typedef struct _EnrollData
   unsigned int  sigint_handler;
   FpFinger      finger;
   int           ret_value;
+  gboolean      update_fingerprint;
 } EnrollData;
 
 static void
@@ -84,7 +85,8 @@ on_enroll_completed (FpDevice *dev, GAsyncResult *res, void *user_data)
       /* Even if the device has storage, it may not be able to save all the
        * metadata that the print contains, so we can always save a local copy
        * containing the handle to the device print */
-      int r = print_data_save (print, enroll_data->finger);
+      int r = print_data_save (print, enroll_data->finger,
+                               enroll_data->update_fingerprint);
       if (r < 0)
         {
           g_warning ("Data save failed, code %d", r);
@@ -124,6 +126,40 @@ on_enroll_progress (FpDevice *device,
           fp_device_get_nr_enroll_stages (device));
 }
 
+static gboolean
+should_update_fingerprint (void)
+{
+  int update_choice;
+  gboolean update_fingerprint = FALSE;
+
+  printf ("Should an existing fingerprint be updated instead of being replaced (if present)? "
+          "Enter Y/y or N/n to make a choice.\n");
+  update_choice = getchar ();
+  if (update_choice == EOF)
+    {
+      g_warning ("EOF encountered while reading a character");
+      return EXIT_FAILURE;
+    }
+
+  switch (update_choice)
+    {
+    case 'y':
+    case 'Y':
+      update_fingerprint = TRUE;
+      break;
+
+    case 'n':
+    case 'N':
+      update_fingerprint = FALSE;
+      break;
+
+    default:
+      g_warning ("Invalid choice %c, should be Y/y or N/n.", update_choice);
+      return EXIT_FAILURE;
+    }
+  return update_fingerprint;
+}
+
 static void
 on_device_opened (FpDevice *dev, GAsyncResult *res, void *user_data)
 {
@@ -139,13 +175,26 @@ on_device_opened (FpDevice *dev, GAsyncResult *res, void *user_data)
       return;
     }
 
-  printf ("Opened device. It's now time to enroll your finger.\n\n");
+  printf ("Opened device.\n");
+
+  if (fp_device_has_feature (dev, FP_DEVICE_FEATURE_UPDATE_PRINT))
+    {
+      printf ("The device supports fingerprint updates.\n");
+      enroll_data->update_fingerprint = should_update_fingerprint ();
+    }
+  else
+    {
+      printf ("The device doesn't support fingerprint updates. Old prints will be erased.\n");
+      enroll_data->update_fingerprint = FALSE;
+    }
+
+  printf ("It's now time to enroll your finger.\n\n");
   printf ("You will need to successfully scan your %s finger %d times to "
           "complete the process.\n\n", finger_to_string (enroll_data->finger),
           fp_device_get_nr_enroll_stages (dev));
   printf ("Scan your finger now.\n");
 
-  print_template = print_create_template (dev, enroll_data->finger);
+  print_template = print_create_template (dev, enroll_data->finger, enroll_data->update_fingerprint);
   fp_device_enroll (dev, print_template, enroll_data->cancellable,
                     on_enroll_progress, NULL, NULL,
                     (GAsyncReadyCallback) on_enroll_completed,
@@ -171,11 +220,9 @@ main (void)
   FpDevice *dev;
   FpFinger finger;
 
-  g_print ("This program will enroll the selected finger, unconditionally "
-           "overwriting any print for the same finger that was enrolled "
-           "previously. If you want to continue, press enter, otherwise hit "
-           "Ctrl+C\n");
-  getchar ();
+  g_print ("This program will enroll the selected finger overwriting any print for the same"
+           " finger that was enrolled previously. Fingerprint updates without erasing old data"
+           " are possible on devices supporting that. Ctrl+C interrupts program execution.\n");
 
   g_print ("Choose the finger to enroll:\n");
   finger = finger_chooser ();

examples/storage.c

@@ -102,8 +102,23 @@ save_data (GVariant *data)
   return 0;
 }
 
+static FpPrint *
+load_print_from_data (GVariant *data)
+{
+  const guchar *stored_data = NULL;
+  gsize stored_len;
+  FpPrint *print;
+
+  g_autoptr(GError) error = NULL;
+  stored_data = (const guchar *) g_variant_get_fixed_array (data, &stored_len, 1);
+  print = fp_print_deserialize (stored_data, stored_len, &error);
+  if (error)
+    g_warning ("Error deserializing data: %s", error->message);
+  return print;
+}
+
 int
-print_data_save (FpPrint *print, FpFinger finger)
+print_data_save (FpPrint *print, FpFinger finger, gboolean update_fingerprint)
 {
   g_autofree gchar *descr = get_print_data_descriptor (print, NULL, finger);
 
@@ -137,25 +152,12 @@ print_data_load (FpDevice *dev, FpFinger finger)
 
   g_autoptr(GVariant) val = NULL;
   g_autoptr(GVariantDict) dict = NULL;
-  const guchar *stored_data = NULL;
-  gsize stored_len;
 
   dict = load_data ();
   val = g_variant_dict_lookup_value (dict, descr, G_VARIANT_TYPE ("ay"));
 
   if (val)
-    {
-      FpPrint *print;
-      g_autoptr(GError) error = NULL;
-
-      stored_data = (const guchar *) g_variant_get_fixed_array (val, &stored_len, 1);
-      print = fp_print_deserialize (stored_data, stored_len, &error);
-
-      if (error)
-        g_warning ("Error deserializing data: %s", error->message);
-
-      return print;
-    }
+    return load_print_from_data (val);
 
   return NULL;
 }
@@ -207,16 +209,30 @@ gallery_data_load (FpDevice *dev)
 }
 
 FpPrint *
-print_create_template (FpDevice *dev, FpFinger finger)
+print_create_template (FpDevice *dev, FpFinger finger, gboolean load_existing)
 {
+  g_autoptr(GVariantDict) dict = NULL;
   g_autoptr(GDateTime) datetime = NULL;
   g_autoptr(GDate) date = NULL;
+  g_autoptr(GVariant) existing_val = NULL;
+  g_autofree gchar *descr = get_print_data_descriptor (NULL, dev, finger);
   FpPrint *template = NULL;
   gint year, month, day;
 
-  template = fp_print_new (dev);
-  fp_print_set_finger (template, finger);
-  fp_print_set_username (template, g_get_user_name ());
+  if (load_existing)
+    {
+      dict = load_data ();
+      existing_val = g_variant_dict_lookup_value (dict, descr, G_VARIANT_TYPE ("ay"));
+      if (existing_val != NULL)
+        template = load_print_from_data (existing_val);
+    }
+  if (template == NULL)
+    {
+      template = fp_print_new (dev);
+      fp_print_set_finger (template, finger);
+      fp_print_set_username (template, g_get_user_name ());
+    }
+
   datetime = g_date_time_new_now_local ();
   g_date_time_get_ymd (datetime, &year, &month, &day);
   date = g_date_new_dmy (day, month, year);

examples/storage.h

@@ -21,12 +21,14 @@
 #pragma once
 
 int print_data_save (FpPrint *print,
-                     FpFinger finger);
+                     FpFinger finger,
+                     gboolean update_fingerprint);
 FpPrint * print_data_load (FpDevice *dev,
                            FpFinger  finger);
 GPtrArray * gallery_data_load (FpDevice *dev);
-FpPrint * print_create_template (FpDevice *dev,
-                                 FpFinger  finger);
+FpPrint * print_create_template (FpDevice      *dev,
+                                 FpFinger       finger,
+                                 const gboolean load_existing);
 gboolean print_image_save (FpPrint    *print,
                            const char *path);
 gboolean save_image_to_pgm (FpImage    *img,